1. Field of the Invention
The present invention relates to optical fibers and, in particular, to optical fiber connectors which are used for connecting optical fibers to each other and, more particularly, to ferrules used in optical transmissions with optical connectors to hold optical fibers accurately in an area array for low optical loss across to an adjacent optical fiber array, optical waveguide array, optical transmit array, optical mirror and/or optical receive arrays.
2. Description of Related Art
Optical connectors are used in optical communications to couple optical fibers together so that light transmitting from a bundle of one or more fibers of the connector will pass through the connector assembly to corresponding fibers or other optical input for a device connected to the other end of the connector assembly. A ferrule is typically part of the connector, and it is the part of the connector into which the fibers are inserted before the ferrule is inserted into an overall connector assembly. The ferrule holds the fibers in a precise position and ensures that when a connector assembly is attached to a mating connector assembly or some other device that the fibers of the connector assembly are held in consistent alignment. See for example, U.S. Pat. Nos. 6,422,760; 6,439,778; 6,604,866; 6,616,343; and 6,628,000, which patents are hereby incorporated by reference.
An optical fiber positioning member such as a ferrule requires a high dimensional accuracy since they are required to carry out positioning of the respective axial centers of optical fibers to be butted against each other at a high accuracy and also demand a high dimensional stability when they are used over a long period of time. Broadly stated, unlike an electrical connector, an optical fiber connector is required to align exactly the opposed ends of two optical fibers to be connected. The problems however, with known connectors for connecting a plurality of optical fibers is potential misalignment, side loading, and torque in the connection.
In general, ferrules are adapted for the insertion of the leading end of optical fibers to be connected and the connection of two optical fibers is attained by abutting two such ferrules against each other. Specifically, two ferrules each having a leading end of an optical fiber inserted and affixed therein are abutted against each other thereby aligning the axes of the optical fibers. Typically the ferrule is mounted in a connector housing and the outer end face of the ferrule is exposed for face-to-face contact with the ferrule end face of the mating opposite half of the connector. Typically, an optical fiber has about a 125 micron coated diameter and the openings are spaced from each other on the center-to-center spacing (“pitch”) of 250 microns.
Conventional ferrules are molded in plastic or epoxy in a 1 by 12 or 2 by 12 array using a common molding technique called transfer molding. However, there is an increasing need among users in the fiber optic field for larger groups of fiber arrays. A small array containing ferrule molded out of epoxy or plastic can conventionally be made but special care must be taken during fabrication when the array becomes larger. Plastic molding technology is very process sensitive for molds having a requisite precision and even small arrays are extremely difficult to make. Additionally, since they are made from organic materials which generally have a large coefficient of thermal expansion, they can be impacted by changes in temperature.
Accordingly, as the array size increases, yield tends to be poor due to the inherent manufacturing process errors that occur in plastics molding. Since the tolerances on these ferrules must be very accurate, high yield manufacture is very difficult when the array size necessitates two rows and exceptionally difficult for more than two rows. Additionally, making ferrules for larger arrays is even more difficult if the holes approach the periphery of the ferrule since the structural integrity of the peripheral walls decreases. In addition, process variations during production cause parts to also have poor tolerance at the periphery. Also, for organic materials and larger connector sizes (for large arrays of optical connections) the distance to neutral point has increased sensitivity to temperature changes and optical loss for connections at the periphery and greatest DNP. In addition, the use of ceramic and/or silicon based reference support for connectors can provide not only X-Y dimensional integrity for the connector but also coplanarity in z direction between mating connector faces to minimize loss between corresponding optical channels compared to other materials used at the connector interface.